BLASTBufferQueue: Fix unnecessary copying of Surface

When we call mSurface.transferFrom(getOrCreateBLASTSurface()) we
always end up incrementing mSurface.generationId, because
BLASTBufferQueue.java::getSurface will always return a new native
wrapper object. We had a similar situation with
mSurface.copyFrom(mSurfaceControl), and had to build IGBP
comparison in to the native method. Here though, it's easier
to just rely on the stability of the Surface (never changes
for the lifetime of the BLASTBufferQueueAdapter) to avoid
duplicate calls to transferFrom.

Bug: 152501005
Test: Existing tests pass.
Change-Id: I64b9a6ae3cabfa75974e040460638417bfac6845

core/java/android/view/ViewRootImpl.java

@@ -1748,13 +1748,17 @@ public final class ViewRootImpl implements ViewParent,
             return null;
         }
 
+        Surface ret = null;
         if (mBlastBufferQueue == null) {
             mBlastBufferQueue = new BLASTBufferQueue(
                 mBlastSurfaceControl, width, height);
+            // We only return the Surface the first time, as otherwise
+            // it hasn't changed and there is no need to update.
+            ret = mBlastBufferQueue.getSurface();
         }
         mBlastBufferQueue.update(mBlastSurfaceControl, width, height);
 
-        return mBlastBufferQueue.getSurface();
+        return ret;
     }
 
     private void setBoundsLayerCrop() {
@@ -7349,8 +7353,14 @@ public final class ViewRootImpl implements ViewParent,
             if (!mUseBLASTAdapter) {
                 mSurface.copyFrom(mSurfaceControl);
             } else {
-                mSurface.transferFrom(getOrCreateBLASTSurface(mSurfaceSize.x,
-                        mSurfaceSize.y));
+                final Surface blastSurface = getOrCreateBLASTSurface(mSurfaceSize.x,
+                    mSurfaceSize.y);
+                // If blastSurface == null that means it hasn't changed since the last time we
+                // called. In this situation, avoid calling transferFrom as we would then
+                // inc the generation ID and cause EGL resources to be recreated.
+                if (blastSurface != null) {
+                    mSurface.transferFrom(blastSurface);
+                }
             }
         } else {
             destroySurface();